Pathology of the Head and Neck

152 S. Di Palma · R.H.W. Simpson · A. Skalova · I. Leivo5Fig. 5.43. Basal cell adenocarcinoma. In spite of the lack of significantcellular atypia, the infiltrative pattern is diagnostic of malignancy.Courtesy of Prof. J.W. Eveson, Bristol, UKamount of basement membrane material varies, butcan be marked, especially in the membranous variant.Occasional cases show cytological pleomorphism, butgenerally this is absent, and mitotic figures are usuallysparse. The most reliable indicator of malignancy is infiltrationof the surrounding gland, and less frequentlyof blood vessels and nerves (Fig. 5.43) [16]. In addition,the Ki-67 proliferation index is usually higher in basalcell adenocarcinoma than its benign counterpart (>5%vs.